Simulations of CO$_{2}$ adsorbed on a bundle of carbon nanotubes*

Using the method of grand canonical Monte Carlo (GCMC), we simulated the adsorption of CO$_{2}$ in a bundle of closed carbon nanotubes, for temperatures between 74K and 240K. From the outcome of the simulations, we computed the isosteric heat of adsorption, qst. The results are summarized as follows: 1) at low temperature the adsorption isotherms display two steps, which correspond to adsorption in the groove and monolayer completion respectively; 2) at a higher temperature, these steps are smoothed away; 3) at low coverage (up to one monolayer), the qst has the same behavior as for other gases (Ar, Kr) while at higher coverage, it differs from experimental findings. In our simulation the nanotubes were considered smooth, rigid hollow cylinders made of carbon with the density of graphene. The interaction CO$_{2}$--NT was computed as the integration of a Lennard-Jones potential plus the CO$_{2}$-C quadrupole-quadrupole energy.